'Ayakashi' is a broad term in Japanese used to describe nearly all monsters and supernatural beings from folklore, including some creatures from European folklore. Another known word for them is Yokai (妖 is yo = “mysterious, bewitching, unearthly, weird” and 怪 is kai = “mystery, wonder, strange.” The term 'yokai' does not always necessarily mean 'monster'). The Ayakashi vary from malevolent, mischievous tricksters to creatures that bring fortune and luck to those they encounter. Their appearance ranges from animalistic to that of a regular human, from regular household inanimate objects to strange shapes that can't be described.'
Hengen is the term for shapeshifters. Most of the Greater Ayakashi are Hengen, shapeshifting to look like regular human beings. It is easiest for the Tengu and the Kitsune to shapeshift their forms –the theory for this is that the Tengu and Kitsune were originally human beings who had once in their lifetime been possessed by either Hengen and so, every time they reincarnate, it is in the form of the Hengen they were possessed by. The Lesser Ayakashi, known as Yori Chiisai, are not as powerful and cannot shapeshift like the Hengen can.